1. Field of the Invention
Embodiments of the invention include polymeric compounds, and compositions including such compounds, that may be used in forming barrier layers for protecting underlying materials and structures and methods of utilizing such compounds and compositions. For example, compounds and compositions according to example embodiments of the invention may be used in manufacturing semiconductor integrated circuits, particularly with respect to methods for forming photoresist barrier layers and/or patterns that will provide satisfactory protection for underlying materials and structures while also simplifying the subsequent removal processes.
2. Description of the Related Art
In fabrication processes used for manufacturing semiconductor devices, photolithographic processes are used repeatedly to form a wide variety of films and patterns at different stages of the fabrication process. As semiconductor devices have become more highly integrated, the critical process dimensions, for example, the spacing between adjacent conductive lines, are being reduced accordingly. The increased degree of integration has led to other changes in the fabrication process as well including, for example, delaying formation of capacitor structures until after formation of the bit lines in semiconductor memory devices such as DRAMs to provide additional surface area for capacitor formation. The processes developed for forming capacitor structures typically include a series of sacrificial and barrier layers that are used in combination with one or more of deposition, planarization and etch processes to obtain the desired structure(s).
Due to the technical requirements associated with achieving higher degrees of integration in semiconductor devices, there has been continuing emphasis on reducing the surface area required for forming a memory cell in semiconductor memory devices. These efforts have led to difficulties in forming capacitors having a sufficient storage capacitance within the memory cell. Various methods have been proposed and/or adopted for maintaining the capacitance of such storage capacitors at acceptable levels in a reduced cell area. One approach involves increasing the height of the storage node by, for example, increasing the height of the lower electrode of a capacitor to form what is widely referred to as a cylindrical capacitor.
Examples of such cylindrical capacitor structures are disclosed in U.S. Pat. Nos. 6,700,153 and 6,171,902, the disclosures of which are hereby incorporated, in their entirety, by reference to the extent consistent with the present disclosure.
One such conventional method for fabricating a type of One Cylinder Storage (OCS) capacitor that can be used, for example, as the charge storage device in a DRAM memory cell, is illustrated in FIGS. 1A-1E. As illustrated in FIG. 1A, a substrate is prepared with both insulating regions 1, for example, an interlayer oxide, and a conductive regions 2, such as a contact plug or a pad plug for establishing electrical contact with conductive regions formed below the conductive regions.
A stop layer 3 may then be formed on both the insulating regions and conductive regions 2, with a molding layer 4, typically formed from an insulating material, for example, a silicon oxide, then being formed on the etch stop layer 3. The molding layer is then patterned and etched using a suitable photolithographic process (not shown) to remove the molding layer 4 and the stop layer 3 from regions of the substrate to form an opening 6 and thereby expose an upper surface of the conductive region 2. This opening 6 formed in the molding layer will, in turn, serve as the “mold” pattern for the subsequently formed capacitor structure. The photoresist pattern used as an etch mask (not shown) is then removed and the exposed surfaces cleaned in preparation for additional processing.
One or more layers of conductive material 7, 8, for example, a primary conductive layer may be combined with a barrier layer and/or an adhesion promoting layer in order to form a multilayer conductive stack structure having a desired combination of properties. One such combination of materials used for forming conductive material layers 7, 8 is a metal and the corresponding metal nitride. The conductive material layer(s) are formed on the exposed surfaces of the mold pattern structure including the upper surface of the remaining portions of the molding layer 4, the sidewalls of the opening 6 and the surface of the conductive region 2 exposed at the bottom of the opening. As illustrated in FIG. 1B, an insulating buffer layer 10, for example, a CVD oxide, is then formed on the conductive material 7, 8 to a thickness sufficient to fill the opening 6. As the aspect ratio of the opening 6 increases, however, the chance that the deposition will seal the mouth of the opening before completely filling the opening increases. In such instances, a generally centrally located void 12 will remain within the opening 6.
As illustrated in FIG. 1C, the upper portion of the insulating buffer layer 10 can be removed using any suitable blanket etch or chemical mechanical polishing (CMP) method to expose an upper surface of the conductive material 7, 8. As illustrated in FIG. 1D, the upper portion of the conductive material layers 7, 8 and additional upper portions of the insulating buffer layer 10 can then be removed using any suitable method (or combination of methods) including, for example, blanket dry (plasma) etch-back or CMP processing, thereby leaving only those portions of the insulating buffer layer 10 and the conductive material layers 7, 8 that were in the remaining portion of the opening 6.
As illustrated in FIG. 1E, the remaining portions of the molding layer 4 and the insulating buffer layer 10 are then removed either simultaneously with an appropriate etch, for example a wet etch using a low ammonium fluoride liquid (LAL) etch composition or sequentially using a sequence of suitable etch compositions and/or methods. During removal of these layers, the remaining portion of the void 12 may complicate the processing by effectively reducing the thickness of the insulating buffer layer 10 relative to the remaining portions of the molding layer 4.
Depending on the combination of conductive layer 7, 8 composition, insulating buffer layer 10 composition and the etch chemistry or chemistries utilized to remove these layers, the central portion of the conductive layers 7, 8 above the conductive region 2 may be exposed to the etch composition for an extended period of time, thereby increasing the possibility that one or more of the layers will be damaged, contaminated or breached. In such instances, the initial yield and/or the reliability of the resulting devices may be degraded. After the remaining portions of the molding layer 4 and the insulating buffer layer 10 have been removed, the remaining structures, in particular the lower electrode of the capacitor, make be cleaned to remove residual etch composition and water, for example, a sequence of deionized water (DI) rinses to a target resistivity followed by processing in an isopropyl alcohol (IPA) dryer.
Another conventional method for fabricating OCS capacitors that can be used, for example, as the charge storage device in a DRAM memory cell, is illustrated in FIGS. 2A-2G. As in FIG. 1 and as again illustrated in FIG. 2A, a substrate is prepared with both insulating regions 1, for example, an interlayer oxide, and a conductive regions 2, such as a contact plug for establishing contact with conductive regions formed below the conductive regions.
A stop layer 3 may then be formed on both the insulating regions and conductive regions 2, with a molding layer 4, typically formed from an insulating material, for example, a silicon oxide, then being formed on the etch stop layer 3. The molding layer is then patterned and etched using a suitable photolithographic process (not shown) to remove the molding layer 4 and the stop layer 3 from regions of the substrate to form an opening 6 and thereby expose an upper surface of the conductive region 2. This opening 6 formed in the molding layer will, in turn, serve as the “mold” pattern for the subsequently formed capacitor structure. The photoresist pattern used as an etch mask (not shown) is then removed and the exposed surfaces cleaned in preparation for additional processing.
One or more layers of conductive material 7, 8, for example, a primary conductive layer may be combined with a barrier layer and/or an adhesion promoting layer in order to form a multilayer conductive stack structure having a desired combination of properties. One such combination of materials used for forming conductive material layers 7, 8 is a metal and the corresponding metal nitride. The conductive material layer(s) are formed on the exposed surfaces of the mold pattern structure including the upper surface of the remaining portions of the molding layer 4, the sidewalls of the opening 6 and the surface of the conductive region 2 exposed at the bottom of the opening. As illustrated in FIG. 2B, a photoresist buffer layer 14, for example, a novolak (also widely referred to as “novolac” in the art) resin-based photoresist, is then formed on the conductive material 7, 8 to a thickness sufficient to fill the opening 6. Through selection of an appropriate photoresist composition in combination with an appropriate application technique, the photoresist buffer layer 14 may be formed without incurring the voids associated with depositions of inorganic materials and illustrated in FIGS. 1B-1D, for example, CVD silicon oxide depositions, even in higher aspect ratio openings 6.
As illustrated in FIG. 2C, an upper portion 14a of the photoresist buffer layer 14 can then be removed by exposing the upper portion of the photoresist buffer layer to radiation having a combination of frequency and intensity that will tend to breakdown or depolymerize the upper portion 14a of the photoresist buffer layer 14 relative to the lower portion 14b of the buffer layer. This exposed portion of the photoresist buffer layer can then be removed by using a suitable developing solution, typically an alkaline solution for positive photoresist compositions. As illustrated in FIG. 2D, after removing the upper portion 14a of the photoresist buffer layer 14, a lower portion 14b of the photoresist buffer layer will remain in the opening 6 while upper portions of the conductive layers 7, 8 are exposed. The lower portion 14b of the photoresist buffer layer can then be baked or cured at a temperature and for a bake duration sufficient to harden the lower portion 14b in order to increase its resistance to the etch solutions used to remove the remaining portions of the molding layer 4.
As illustrated in FIG. 2E, any suitable blanket etch or CMP method may then be utilized to remove an upper portion(s) of the conductive material 7, 8 using any suitable method (or combination of methods) including, for example, blanket dry (plasma) etch-back or CMP processing, thereby leaving only those portions of the photoresist buffer layer 14 and the conductive material layers 7, 8 that were in the remaining portion of the opening 6.
As illustrated in FIG. 2F, the remaining portions of the molding layer 4 can then be removed with an appropriate etch, for example, a wet etch using a LAL etch composition, while the lower portion 14b of the photoresist buffer layer 14 serves as an etch mask to protect the lower portions of the conductive material layers 7, 8 and the underlying conductive region 2. As illustrated in FIG. 2G, the lower portion 14b of the photoresist buffer layer 14 may then be removed with a conventional ashing process during which the organic photoresist is exposed to a combination of elevated temperatures and/or activated oxygen species in order to “burn” the lower portion 14b of the resist out of the opening 6. The “ashed” substrate is then typically subjected to a clean-up process to remove residual photoresist and/or particulate contamination before the subsequent processing necessary to complete the capacitor structure.
This second conventional method, therefore, by reducing the likelihood of voids within the buffer material provided within the opening 6, improves the degree of protection afforded the conductive material layers 7, 8 from the etch composition(s) being used to remove the molding layer 4, thereby reducing the possibility that one or more of the layers will be damaged, contaminated or breached.
The conventional novolak photoresist compositions typically include three basic ingredients, specifically 1) a phenolic novolak resin, 2) a diazonaphthoquinone (DNQ) type dissolution inhibitor, and 3) an organic solvent. The novolak resin is utilized primarily for establishing the basic physical properties of the resulting photoresist film, for example, good film forming characteristics, etch resistance and thermal stability. The DNQ component, however, is utilized for modifying the relative dissolution rate of the exposed and unexposed regions of the novolak photoresist film in conventional alkaline developing solutions and allowing a useful photoresist pattern to be developed from the exposed photoresist film. The organic solvent(s) included in the photoresist composition are selected to provide appropriate viscosity control for the photoresist composition to allow the production of uniform, glassy thin photoresist films by, for example, spin coating techniques.
Novolak resins are soluble in a variety of common organic solvents including, for example, cyclohexanone, acetone, ethyl lactate, NMP (1-methyl-2-pyrrolidinone), diglyme (diethyleneglycol dimethyl ether), and PGMEA (propyleneglycol methyl ether acetate). Commercial photoresists are generally Formulated with polymer loadings of 15 to 30 weight percent with respect to the solvent content of the resist composition with the viscosity of the solution being adjusted by varying the polymer to solvent ratio of the composition, thereby allowing different photoresist compositions to be Formulated for generating a variety of film thicknesses.
The addition of DNQ inhibitors to novolak resins retards the dissolution rate of the photoresist film with an increasing concentration of the DNQ inhibitor(s) tending to further retard the dissolution rate. Upon exposure to radiation of appropriate frequency and intensity, however, the DNQ-novolak composition will tend to exhibit a dissolution rate greater than the dissolution rate of pure novolak resin. Conventional DNQ-novolak resists may have a DNQ inhibitor content of approximately 20 weight percent with respect to the weight of novolak resin, and can provide a differential dissolution rate of more than three orders of magnitude between the unexposed and exposed states. The nature of the interaction between the DNQ dissolution inhibitors and novolak resins is complex, but experimental evidence has suggested that hydrogen bonding of the inhibitor to the novolak resin plays an important role in inhibiting dissolution of the composition.
The developing solutions used for developing DNQ-novolak photoresist compositions are generally aqueous alkaline solutions. Although the earliest developing solutions used with DNQ-novolak resists were alkali metal hydroxide solutions, for example, dilute KOH or NaOH solutions, as the semiconductor industry has become more sensitive to metal contamination, the use of these metal containing developing solutions has decreased in favor of organic developers, for example, aqueous solutions of tetramethyl ammonium hydroxide (TMAH), typically at a concentration of between 0.2 and 0.3N.
The basic novolak resins include repeating phenol derivative monomer units that may be represented by, for example, the Formula:
and may, in other instances, form complexes with the DNQ inhibitor compounds, for example, derivatives of 4- and 5-DNQ sulfonyl chlorides, with may be represented by, for example, the Formula (where r is a halogen):

After the novolak photoresists have been developed and baked or otherwise cured or hardened, the residual portions of the photoresist film may be difficult to remove using conventional ashing processes, thereby increasing the processing time and expense and increasing the likelihood of incomplete removal that could compromise subsequent processing, functional yield and/or the reliability of the resulting devices. Without being bound by theory, it is believed that the prevalence of the C═C bonds in the phenol derivative backbone of the novolak polymer accounts for the film's resistance to conventional ashing processes.
As detailed above, the use of conventional inorganic materials for forming buffer layers, for example, silicon oxides that are formed by one or more CVD processes, tend to exhibit increasing void formation as the aspect ratio (depth/width) of the openings increases. See FIGS. 1A-1E and the corresponding description provided above. The use of conventional inorganic layers will also tend to increase the processing time as a result of the etch back and/or CMP processes necessary to remove the upper portion of the layers.
As also detailed above, the use of conventional novolak-based photoresist compositions for forming buffer layers requires the use of an exposure step in order to breakdown the polymers in the photoresist composition and/or modify their solubility to a degree that will allow them to be removed during a subsequent developing step. See FIGS. 2A-2G and the corresponding description provided above. Conventional novolak-based photoresist compositions are also typically subjected to a relatively high bake temperature on the order of 270° C. in order to harden the photoresist so that it is better suited to endure wet etch solutions without excessive dissolution and contamination of the wet etch bath equipment by the dissolving photoresist layer. This exposure step and the subsequent baking step will both involve additional handling, equipment and processing time, all of which will tend to increase the overall processing cost, the risk of handling induced damage and the overall processing time.